Selenium has been of interest primarily as a result of its cytotoxic effects. However, selenium has also been demonstrated to be an essential trace nutrient. Selenium deficiency has been shown to influence the hepatic metabolism and toxicity of a number of xenobiotics, and the inducibility of microsomal cytochromes P-450. Cytochrome P-450 refers to a family of liver microsomal hemoproteins that catalyze the oxidative metabolism of a wide array of endogenous and exogenous compounds. The goal of this proposal is to define and fully characterize the effects of selenium on the regulation of the induction of cytochromes P-450 by phenobarbital. To achieve this goal, studies with selenium deficient rats will be paralleled by studies utilizing the novel in vitro model system of primary monolayer cultures of adult rat hepatocytes. In hepatocyte culture, the time course and magnitude of selenium loss and repletion will be determined. These results will provide a foundation for the examination of the effects of selenium on the in vitro synthesis and degradation of the phenobarbital induced forms of cytochrome P-450 as determined by specific immunoprecipitation and immunoblot analyses. In hepatocyte culture, the effect of selenium on the expression of the genes for the phenobarbital forms of cytochrome P-450 will be examined by quantitating the level of mRNA directing the synthesis of the phenobarbital forms of cytochrome P-450. Selenium deficiency in vivo has also increased both heme synthesis and degradation. These effects can be reversed upon selenium repletion. This observation will be examined in hepatocyte culture by determining the effect of selenium concentration on the activities of Delta-amino-levulinic acid synthetase and microsomal heme oxygenase. Finally, the role of selenium in the regulation of the selenoenzyme glutathionine-peroxidase will be systematically examined in hepatocyte culture. It is anticipated that the proposed studies will demonstrate primary monolayer cultures of adult rat hepatocytes to be an excellent model system for determining the effect of trace element deficiencies and also provide new information on the induction of cytochromes P-450 by phenobarbital.